1. Technical Field
The present invention relates to an external power supply device for an electronic device, and more particularly to a power supply device having function of heating.
2. Related Art
An electric power for a portable electronic device such as notebook computer can be selectively supplied by an internal power source or an external power source. The internal power source is a battery, such as a rechargeable battery, which is used for providing direct current (DC) power directly to the portable electronic device. The external power source is a power supply device with rectification and voltage transforming functions. The power supply device receives an alternating current (AC) power from an AC socket. Through rectification and voltage transformation, the AC power is transformed into DC power. The DC power is then provided to the portable electronic device and may charge the battery as an internal power source. An electrical capacity of the rechargeable battery is limited. When the AC power is available, a user can use the power supply device to provide the power required for the use of the portable electronic device.
In order to ensure that the user can use the portable electronic device when the user leaves their home or on the road, the user usually takes the power supply device with him/her. For example, when the user carries a notebook computer on a business trip, the user will certainly also take a power supply device for the notebook computer. As most power supply devices have certain weights and volumes, which can occupy certain luggage space, and as a result certain daily necessities cannot be accommodated in a suitcase, resulting in inconvenience when traveling.